U.S. patent number 3,982,214 [Application Number 05/625,344] was granted by the patent office on 1976-09-21 for 180.degree. phase shifting apparatus.
This patent grant is currently assigned to Hughes Aircraft Company. Invention is credited to Richard W. Burns.
United States Patent |
3,982,214 |
Burns |
September 21, 1976 |
180.degree. PHASE SHIFTING APPARATUS
Abstract
The use of electronically variable phase shifters is required in
phased array radar systems. Diode phase shifters are particularly
well suited for use in phased array radar systems because they have
size and weight advantage over other types of phase shifting
components such as ferrite devices and traveling wave tubes and, in
addition, offer the potential of cost reductions through the
application of batch processing techniques. In accordance with the
present invention, a 180.degree. phase bit is provided by two
series diodes with three transmission line segments shunting each
junction to ground through a common shunt diode. Operation is
effected by the simultaneous forward or reverse biasing of the
series and shunt diodes, thereby introducing a 180.degree. phase
difference in a signal transmittal therethrough.
Inventors: |
Burns; Richard W. (Orange,
CA) |
Assignee: |
Hughes Aircraft Company (Culver
City, CA)
|
Family
ID: |
24505632 |
Appl.
No.: |
05/625,344 |
Filed: |
October 23, 1975 |
Current U.S.
Class: |
333/164;
327/256 |
Current CPC
Class: |
H01P
1/185 (20130101); H03H 7/185 (20130101) |
Current International
Class: |
H03H
7/00 (20060101); H03H 7/18 (20060101); H01P
1/18 (20060101); H01P 1/185 (20060101); H03H
007/30 () |
Field of
Search: |
;333/29,31R,7D,7R,97S
;307/262,317,259 ;328/55,56 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Chatmon, Jr.; Saxfield
Attorney, Agent or Firm: Himes; Robert H. MacAllister; W.
H.
Claims
What is claimed is:
1. An apparatus for selectively introducing a predetermined phase
shift in a signal, said apparatus comprising an input terminal and
an output terminal; a first unidirectionally conducting device
connected from said input terminal to an intermediate junction; a
second unidirectionally conducting device connected from said
intermediate junction to said output terminal; first, second and
third segments of transmission line connected from said input
terminal, said intermediate terminal and said output terminal,
respectively, to a common junction, said first, second and third
segments of transmission line each being greater than one-quarter
wavelength and less than one-half wavelength long at the frequency
of said signal; a third unidirectionally conducting device
connected from said common junction to a third junction maintained
at a substantially fixed reference potential; and means coupled to
said first, second and third unidirectionally conducting devices
for simultaneously rendering said first, second and third devices
conductive or non-conductive.
2. The apparatus for selectively introducing a predetermined phase
shift in a signal wherein said predetermined phase shift is of the
order of 180.degree..
3. An apparatus for selectively introducing a predetermined phase
shift in a signal, said apparatus comprising an input terminal and
an output terminal; a first unidirectionally conducting device
connected from said input terminal to an intermediate junction; a
second unidirectionally conducting device connected from said
intermediate junction to said output terminal; first, second and
third segments of transmission line connected from said input
terminal, said intermediate terminal and said output terminal,
respectively, to a common junction, said first, second and third
segments of transmission line each being greater than one-quarter
wavelength and less than one-half wavelength long at the frequency
of said signal; a third unidirectionally conducting device
connected from said common junction to a third junction maintained
at a substantially fixed reference potential; and means coupled to
said first, second and third unidirectionally conducting devices
for selectively and simultaneously forward biasing or reverse
biasing said first, second and third unidirectionally conducting
devices thereby to selectively introduce said predetermined phase
shift in said signal.
4. The apparatus for selectively introducing a predetermined phase
shift in a signal as defined in claim 3 wherein each of said first,
second and third segments of transmission line are of the order of
three-eighths wavelength long at the frequency of said signal.
5. The apparatus for selectively introducing a predetermined phase
shift in a signal as defined in claim 3 wherein each of said first
and third segments of transmission line are of the order of
three-eighths wavelength long at the frequency of said signal, said
second segment of transmission line is disposed in a straight line
configuration between said intermediate junction and said common
junction; and additional means connected to said intermediate
junction for making the effective electrical length of said second
segment of transmission line equal to three-eighths wavelenth at
the frequency of said signal.
6. The apparatus for selectively introducing a predetermined phase
shift in a signal as defined in claim 5 wherein said additional
means constitutes an open circuited stub segment of transmission
line.
7. An apparatus for selectively introducing a predetermined phase
shift in a signal, said apparatus comprising an input terminal and
an output terminal; a first diode connected from said input
terminal to an intermediate junction; a second diode connected from
said intermediate junction to said output terminal; first, second
and third segments of transmission line connected from said input
terminal, said intermediate terminal and said output terminal,
respectively, to a common junction, said first, second and third
segments of transmission line each being greater than one-quarter
wavelength and less than one-half wavelength long at the frequency
of said signal; a third diode connected from said common junction
to a third junction maintained at a substantially fixed reference
potential; and means coupled to said first, second and third diodes
for selectively and simultaneously forward biasing or reverse
biasing said first, second and third diodes thereby to selectively
introduce said predetermined phase shift in said signal.
8. An apparatus for selectively introducing a predetermined phase
shift in a signal, said apparatus comprising an input terminal and
an output terminal; a first diode connected from said input
terminal to an intermediate junction; a second diode connected from
said intermediate junction to said output terminal, said first and
second diodes being poled to allow bias current to flow away toward
said intermediate junction; first, second and third segments of
transmission line connected from said input terminal, said
intermediate junction and said output terminal, respectively, to a
common junction, each of said first, second and third segments of
transmission line being greater than one-quarter wavelength and
less than one-half wavelength long at the frequency of said signal;
a third diode connected from said common junction to ground, said
third diode being poled to allow bias current to flow towards said
common junction; means connected to said intermediate junction for
maintaining said intermediate junction at quiescent ground
potential; and means connected to the cathodes of said first,
second and third diodes for selectively and simultaneously forward
or reverse biasing said first, second and third diodes thereby to
selectively introduce said predetermined phase shift in said
signal.
9. The apparatus for selectively introducing a predetermined phase
shift in a signal as defined in claim 8 wherein each of said first,
second and third segments of transmission line is three-eighths
wavelength long at the frequency of said signal.
10. The apparatus for selectively introducing a predetermined phase
shift in a signal as defined in claim 8 wherein said first and
third segments of transmission line are each three-eighths
wavelength long at the frequency of said signal and said second
segment of transmission line is disposed in a straight line
configuration between said common junction and said intermediate
junction; and means connected to said intermediate junction for
making the electrical equivalent length of said second segment of
transmission line equal to three-eighths wavelength long at the
frequency of said signal.
Description
BACKGROUND OF THE INVENTION
Several types of diode phase shifters have been devised such as
switched line, hybrid coupled, loaded line and three element ".pi."
or "T" circuits. The switched line circuit includes a pair of
single-pole, double-throw switches for switching one of two lengths
of transmission line into a circuit. In general, this circuit
requires four diodes. Phase shift is obtained by switching between
one line used as a reference path and a second line which provides
a delay path. The hybrid coupled circuit includes a 3-decible
hybrid with a pair of balanced diode switches connected to
identical split arms of the hybrid. The hybrid coupled bit is used
extensively because it achieves larger phase shifts while still
using only two diodes. The loaded line circuit includes a number of
pairs of switched susceptances spaced at one-quarter wavelength
intervals along a transmission line. Phase shift is obtained as the
susceptances are changed from an inductive to a capacitive state.
Phase shift for this circuit is limited to about 45.degree. for a
pair of diodes. Lastly, the .pi.-circuit consists of two shunt
elements and one series element. Phase shift is obtained by
changing the circuit elements between a low-pass and a high-pass
condition. Phase shifts of the order of 90.degree. can be obtained
with this circuit. Three diodes are required for the ".pi." circuit
and the "T" circuit which is a dual of the ".pi." circuit.
SUMMARY OF THE INVENTION
In accordance with the present invention, a 180.degree. phase bit
is provided by first and second oppositely poled series diodes
having an approximately three-eighths wavelength transmission line
segment connected from each junction thereof to a common junction
which is, in turn, shunted to ground by a third diode. Operation is
effected by the simultaneous forward or reverse biasing of the
three diodes. When the diodes are forward biased, a radio frequency
signal flows primarily through the series diodes thereby
introducing a minimum phase shift in the signal. Alternatively,
when the diodes are reverse biased, the radio frequency signal is
caused to flow through the transmission line segments, thereby
introducing a maximum phase shift in the signal. In the latter
case, part of the signal also flows through the reverse biased
series diodes. By adjusting the length and the impedance levels of
the transmission line segments and the impedance of the series
path, matched transmission can be achieved in both bias states.
Transformer sections at the input and output can also be used to
match at the bit. The amount of phase shift between the two bias
states is adjusted by proper choice of diode reactances, impedance
levels and transmission line lengths.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a schematic microstrip circuit diagram of the
180.degree. phase bit apparatus of the present invention;
FIG. 2 illustrates a schematic microstrip circuit diagram of a
180.degree. phase bit apparatus using a straight center leg in the
device of FIG. 1. The electrical length of all three lines is made
identical by adding a shunt open circuited stub to the common
junction of the series diodes;
FIG. 3 shows the electrical equivalent circuit diagram of the
apparatus of FIGS. 1 and 2 when the series and shunt diodes are all
forward biased; and
FIG. 4 shows the electrical equivalent circuit diagram of the
apparatus of FIGS. 1 and 2 when the series and shunt diodes are all
reverse biased.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, there is depicted the 180.degree. phase bit
apparatus of the present invention. In particular, an input
terminal 10 is connected through a series diode 12 to a junction 14
which, in turn, is connected through a series diode 16 to an output
terminal 18, the diodes 12, 16 being poled to allow bias current
flow in directions toward junction 14. In addition, three-eights
wavelength segments of transmission lines 20, 22 are connected from
input output terminals 10, 18, through blocking capacitors 28 and
28' to junction 24. Junction 24 is connected through a shunt diode
26 to ground and through a three-eights wavelength transmission
line segment 30 to junction 14. Shunt diode 26 is poled in a
direction to allow bias current flow towards the junction 24.
Further, the input output terminals 10, 18 respectively are
maintained at quiescent ground potential by means of radio
frequency bias chokes 32 and 32' respectively connected therefrom
to ground. The operation of the device of FIG. 1 is not critically
dependent on the radio frequency parameters of the diodes 12, 16,
26 in that a wide range of diode parameters can be used to give
radio frequency phase shift. By way of example, diodes with a
capacitance of the order of 1.0 picofarads and a resistance of 0.25
ohm have been found to be satisfactory for S-band and L-band
applications. Also, diodes with a capacitance of the order of 0.8
picofarad have been found to be satisfactory for C-band
applications. The circuit operates over a wide frequency band. By
way of example bandwidths of 20 to 30 percent have been achieved at
S-band and C-band. It is also pointed out that transmission line
segments 20, 22, 30 are all of substantially the same length. At
low frequencies, this can be accomplished by configuring the center
line 30 so that it has a serpentine shape as shown schematically in
FIG. 1. At high frequencies, the length-to-width ratio of the
center transmission line 30 prevents this in which case the line 30
is made physically shorter than the lines 20, 22 by capacitive
shunt loading the junction 14 of the series diodes 12, 16 and the
line 30 as shown in FIG. 2.
Biasing the 180.degree. phase bit apparatus of the present
invention is accomplished by maintaining the terminal 24 at an
appropriate direct-current potential. The terminal 24 is directly
connected to the cathodes of diodes 12, 16, 26 and is blocked from
the anodes of diodes 12, 16 by blocking capacitors 28 and 28'. In
each case, the anodes of diodes 12, 16, 26 are maintained at
quiescent ground potential. Biasing apparatus includes, for
example, a source of potential 34 which is referenced to ground so
as to provide a potential of -0.75 volt at a negative terminal 35
and a potential of +100 volts at a positive terminal 36 thereof.
Terminals 35, 36 of the source of potential 34 are connected to
respective inputs 37, 38 of a double-throw single-pole switch 39
which, in turn, has an output 40 that is connected through a
radio-frequency choke 42 to the transmission line 20. Position of
the pole of switch 39 determines the bias applied to the diodes 12,
16, 26; i.e. when the single-pole of switch 39 is in contact with
terminal 37 thereof, the diodes 12, 16, 26 are forward biased by
+0.75 volt and when the single-pole of switch 39 is in contact with
terminal 38 thereof, the diodes 12, 16, 26 are reverse biased by
-100 volts.
Referring to FIG. 3, there is shown the equivalent circuit of the
apparatus of FIG. 1 when the diodes 12, 16, 26 are forward biased
whereby bias current flows therethrough. Bias current flow through
diode 26 effectively radio-frequency grounds junction 24 through
the small inductor 53 whereby transmission line segments 20, 30, 22
reflect an impedance between infinity and zero to the input
terminal 10, junction 14 and output terminal 18, respectively.
Selection of the actual length and characteristic impedance of the
transmission lines 20, 22, 30 will determine the magnitude and type
of this impedance. It is generally known that a short at the end of
a one-quarter wavelength transmission line generates a very high
impedance (theoretically infinite) at the input and that a short at
the end of a half wavelength transmission reflects a short at the
input. Thus, a short or a small inductive reactance at the end of a
three-eights wavelength transmission line generates an impedance at
the input that is a capacitive reactance between these extremes
illustrated by capacitance 44, 45, 46 connected from terminals 10,
18 and junction 14, respectively, to ground. The series diodes 12,
16 on the other hand, being forward biased, provide slightly
inductive paths 48, 49 connecting the input, output terminals 10,
18 with the junction 14. With reference to FIG. 3, a radiofrequency
signal applied to input terminal 10 divides with one part flowing
through transmission line seqments 20, and a second part flowing
through inductances 48 and 49. Since the inductive reactance of
inductor 53 is very low typically approaching a radio frequency
short circuit most of the input signal at terminal 10 flows
directly through inductances 48 and 49 to terminal 18. Only a small
part of the signal flows through transmission line segment 22 past
inductance 53 and through transmission line segment 22 to output
terminal 18. The capacitances 44, 45, 46 and inductances 48, 49
form a network which maintains proper impedance levels and produces
phase shift between terminals 10 and 18.
Referring to FIG. 4, there is shown the equivalent circuit of the
apparatus of FIG. 1 when the diodes 12, 16, 26 are reverse biased,
i.e. when the single-pole of switch 39 is thrown so as to connect
terminals 38 and 40 thereby reverse biasing the diodes 12, 16, 26
with -100 volts. Under these circumstances the diodes 12, 16, 26
present capacitances 50, 51, 52, respectively, to the
radio-frequency signal. A radio-frequency signal applied to input
terminal 10 divides with one part flowing through the transmission
line segments 20, 22, another part flowing through transmission
line segments 20, 30 and capacitance 51, and still another part
flowing through capacitance 50 and transmission line segments 30,
22 to the output terminal 18. These signal parts recombine at
terminal 18 to form an output signal. The net change in phase shift
for the device is the difference in phase shift between terminals
10 and 18 when the diodes 12, 16, 26 are in forward and reverse
bias. The 180.degree. phase bit device described herein allows wide
tolerance variation in diode 12, 16, 26 parameters since the phase
shift is achieved primarily by proper choice of lengths of the
transmission line segments 20, 22, 30 and impedance levels and is
capable of operating over a bandwidth of the order of 20 to 30
percent. By proper choice of parameters of the diodes and
transmission line segments, phase shifts from very low to
comparatively high values (i.e. greater than 180.degree.) can be
achieved.
Referring to FIG. 2, there is shown the 180.degree. phase bit
circuit of FIG. 1 wherein the transmission line segment 30 has been
replaced by a shorter but straight transmission line segment 60
together with a shunt open circuited transmission line stub 62
connected to junction 14. Other reference numerals refer to
identical elements as described in connection with FIG. 1. The
straight transmission line segment 60 together with stub 62 are
particularly desirable at higher frequencies when implementing the
device with strip line or microstrip. The open circuited stub 62 is
chosen to produce the same effective length with transmission line
segment 60 as was the transmission line segment 30 of the apparatus
of FIG. 1 whereby the operation is the same.
* * * * *